Japanese Patent Application Laid-Open Publication No. 118935/1993 discloses a semiconductor force sensor including a semiconductor force sensor element having a diaphragm section and a sphere for transmitting a force to the diaphragm section. The semiconductor force sensor warps the diaphragm section by the force applied to the sphere and converts a change in this force to an electric signal, thereby measuring the force applied to the sphere or turning on or off a switch. In the semiconductor force sensor, a recess section, in which the sphere is placed, is formed in the central portion of the semiconductor force sensor element, and a through hole, into which the sphere to fitted, is formed in the opposed wall section of an receiving case facing the recess section so that part of the sphere faces outside. With this structure, positioning of the sphere is achieved by the through hole in the opposed wall section with the sphere being secured in the semiconductor force sensor element.
In such a semiconductor force sensor, however, when a force in a direction other than a direction orthogonal to the diaphragm section is transmitted to the diaphragm section through the sphere, an undue force is applied to the diaphragm section, so that the diaphragm section might be broken. Further, a force applied to the direction orthogonal to the diaphragm section could not be measured accurately.
Japanese Utility Model Application No. 38779/1987 (Japanese Utility Model Application Laid-Open publication No. 146734/1988) relating to a microfilm discloses a pressure-sensitive sensor including a sensor element constituted by a thin plate fixed to a receiving case and a composite piezoelectric sheet having electrodes, and a sphere for transmitting a force to the thin plate. The pressure-sensitive sensor applies the force on the sphere to the composite piezoelectric sheet through the thin plate, converts a change in this force to an electric signal, and measures a pressure applied to the sphere. In this pressure-sensitive sensor, a through hole into which the sphere is fitted is formed in the opposed wall section of the receiving case facing the thin plate so that part of the sphere faces outside. With this structure, positioning of the sphere is achieved by the through hole in the opposed wall section with the sphere being in contact with the thin plate.
However, the sensor element in this pressure-sensitive sensor is energized against the sphere through the thin plate by a spring. Thus, the sphere is strongly abutted onto the edge of the through hole in the receiving case. For this reason, when a force in a direction other than the direction orthogonal to the thin plate is transmitted to the thin plate through the sphere, most of the force (force including even the force in the direction other than the direction orthogonal to the thin plate) is measured. Then, there was a problem that the force applied to the direction orthogonal to the thin plate could not be accurately measured.
An object of the present invention is to provide a semiconductor force sensor that can prevent an undue force from being applied to a diaphragm section therein, and thus can prevent the diaphragm section being broken.
Another object of the present invention is to provide a semiconductor force sensor that can accurately measure a force applied to a direction orthogonal to the diaphragm section.